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1.
Solid-state reactions between sodium hydride and sodium hydroxide are unusual among hydride-hydroxide systems since hydrogen can be stored reversibly. In order to understand the relationship between hydrogen uptake/release properties and phase/structure evolution, the dehydrogenation and hydrogenation behavior of the Na-O-H system has been investigated in detail both ex- and in-situ. Simultaneous thermogravimetric-differential thermal analysis coupled to mass spectrometry (TG-DTA-MS) experiments of NaH-NaOH composites reveal two principal features: Firstly, an H2 desorption event occurring between 240 and 380 °C and secondly an additional endothermic process at around 170 °C with no associated weight change. In-situ high-resolution synchrotron powder X-ray diffraction showed that NaOH appears to form a solid solution with NaH yielding a new cubic complex hydride phase below 200 °C. The Na-H-OH phase persists up to the maximum temperature of the in-situ diffraction experiment shortly before dehydrogenation occurs. The present work suggests that not only is the inter-phase synergic interaction of protic hydrogen (in NaOH) and hydridic hydrogen (in NaH) important in the dehydrogenation mechanism, but that also an intra-phase Hδ+… Hδ– interaction may be a crucial step in the desorption process. 相似文献
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Stuart A. Batterman Alfred Franzblau Nanzheng Zhou 《International archives of occupational and environmental health》1996,68(4):268-274
Dermal exposures of methanol were administered in a clinical study designed to compare several biological indicators. Four
subjects were exposed in five exposure sessions of varying length. In each session, a sequence of measurements of methanol
concentrations in blood, breath, and headspace samples of air at exposed and unexposed skin were collected before and after
dermal exposures. Skin headspace samples, collected in gas sampling bags, were designed to reflect equilibrium skin: air partitioning.
At exposed skin, headspace samples were highly elevated for at least 8 h following exposure, indicating the presence of a
methanol reservoir in skin. After exposure, methanol concentrations at exposed skin showed a rapid initial decline, then a
slower first-order decrease. Methanol concentrations were clearly detectable in headspace samples at unexposed skin. Substantial
transfer from exposed skin occurred due to mechanical contact and washing. When transfer was restricted, surface concentrations
at unexposed skin were similar to levels in breath and were strongly correlated to methanol concentrations in blood. While
results are preliminary due to the small sample sizes and several unresolved experimental issues, the simple, rapid, and noninvasive
skin headspace measurements appear useful as a biological exposure indicator that clearly shows the presence and site of a
dermal exposure, and measurements at unexposed skin reflect concentrations in blood.
Received: 14 March 1995/Accepted: 3 November 1995 相似文献
5.
ISABELLA L. KARLE JUDITH L. FLIPPEN-ANDERSON THEODOR WIELAND 《Chemical biology & drug design》1989,33(6):422-427
The synthetic perhydrogenated symmetric analog of the cyclic decapeptide antamanide is biologically inactive, although the conformation of the molecule and the crystal packing are very similar to that of the active symmetric analog of antamanide. In fact, the same conformation for the molecule has now been found in six polymorphs of uncomplexed antamanide and its analogs. The differences between the active and inactive antamanide analogs are displayed dramatically in the conformations of their metal ion (Na+ or Li+) complexes, thus suggesting strongly that for physiological activity antamanide is not in the conformation assumed by the uncomplexed molecule, but rather in the conformation assumed by the complexed state of natural antamanide. The present structure crystallizes in space group P212121 with a = 20.515(14) Å, b = 21.316(16) Å, c = 17.128(16) Å and four peptide molecules in the unit cell. There are three cocrystallized water molecules at full occupancy intrinsic to the peptide, and several more water molecules or other solvent molecules at partial occupancy. The formula of the peptide is C66 H106 N10O10· 4-H2O·2X. 相似文献
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3种常用低温灭菌方法研究现状 总被引:5,自引:2,他引:3
阐述了环氧乙烷低温灭菌法、低温蒸汽甲醛灭菌法、过氧化氢等离子体灭菌法的灭菌机制、主要特点及应用范围。 相似文献
7.
F. H. M. Mikx 《Oral microbiology and immunology》1997,12(4):249-253
The effect of pH, redox potential, O2 and H2 on the growth and proteolytic activity of Treponema denticola ATCC 33520 was studied in a chemostat at different growth rates. The peptidase and protease activities were estimated using different amido-methyl coumarin derivatives and azocasein. The maximum growth rate of T. denticola ATCC 33520 was 0.14 h−1 . Reduction of the growth rate of T. denticola by 50–60% gave: an increase in cell mass of 150–200%, a higher acetogenesis and a shift of the pH optimum. The protease and phenylalanine peptidase activities seemed to be of greater importance for the growth of T. denticola ATCC 33520 than the rather low arginine and proline peptidase activities. The redox potential (Eh ) played a secondary role. At microaerophilic conditions with 1–5% O2 , the cultures maintained a redox potential below −311 mV and an optimal acetogenesis. The presence of H? induced a marked growth stimulation of T. denticola ATCC 33520. It is concluded that the cell mass and proteolytic activity of T. denticola ATCC 33520 are modulated by the growth rate and the pH and to a lesser extend by the redox potential and presence of O2 . Stagnation of the exudate-flow influences these factors and will lead to an increase of the spirochetal population and proteolysis in the periodontal pocket. 相似文献
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The crystal structures of the 1:1 complexes methylguanidinium benzylhydrogenmalonate, (C2N3H8)+(C10H9O4)?, MGD.BMAL, and methylguanidinium ethylhydrogenmalonate, (C2N3H8)+(C5H7O4)?, MGD.EMAL, and of the 2:1 complex methylguanidinium sulfate, (C2N3H8)2SO4, have been determined from three-dimensional X-ray data. For MGD.BMAL, the complex crystallizes in the triclinic space group P with two formula units in a cell of dimensions a = 6.277(5), b = 8.470(3), c = 13.191(6)Å, α= 91.01(1), β= 99.64(9), γ= 90.83(5)°. The structure has been refined to a final value of R = 0.061 based on 1511 intensities. The MGD.EMAL complex is also triclinic, space group P with two molecules in a cell of dimensions a = 9.254(7), b = 9.625(6), c = 6.778(2) Å, α= 109.6(1), β= 100.8(1), γ= 62.7(1)Å. The crystals of this compound are of low quality, and the final value is R = 0.109 based on 706 intensities. (MGD)2SO4 is orthorhombic, space group P212121, with four molecules in a cell of dimensions a = 7.100(4), b = 12.151(3), c = 13.108(2) Å. Refinement has converged to R = 0.054 based on 907 data. All three crystals exhibit extensive interionic hydrogen bonding. The hydrogen bonding in MGD.BMAL includes a Type B interaction and a Type 1 interaction, the latter being a pairwise interaction from both amino nitrogen atoms on the cation to two carboxylate oxygen atoms from the two different carboxylate groups in an anion. In MGD.EMAL, the anion participates in both a Type A and a Type B pairwise interaction with two neighboring cations. The possible implications of the hydrogen bonding patterns in these two compounds for the role of arginyl side chains in protection of γ-carboxyglutamate residues from decarboxylation are discussed. 相似文献